Avaliação do impacto ambiental de efluentes de estações de tratamento de esgotos em corpos receptores no Estado da Paraíba.

Abstract

Impaired water quality of many surface water bodies has aggravated the problem of scarcity and raises the treatment cost to produce water with potable quality for human consumption. This study aimed to evaluate the efficiency of 08 (eight) sewage treatment plants (STP's) in the municipalities of Paraiba State (Joao Pessoa, Sape, Guarabira, Campina Grande, Patos, Itaporanga, Sousa and Cajazeiras) and the environmental impact caused by those final effluents discharges on the quality of receiving water -bodies. The experimental period comprised the period from ago/2000 to may/2004 with monthly collections of samples of raw sewage (RS), final effluent (FE), up and downstream Physical, chemical and microbiological variables were analyzed in the water samples to monitoring and characterize the STP's. Data base were submitted to statistical analysis. The results for both final effluent quality and the receiving body water quality were compared to Brazilian legislation. In order to evaluate it possible utilization in crop irrigation the software - Qualigraf (Beta) was applied on data water quality from downstream sampling point. Algae blooms were frequent in facultative ponds with direct effects on BOD, COD and TSS, as well as water hyacinth in Itaporanga STP with positive influence on treatment efficiency. The rainy season contributed to decrease the STP's performance specially on BOD and COD efficiency but algae biomass have also interfered on the results. Ammonia and total phosphorous removal rates were low, with some exceptions, not exceeding 60 and 30% efficiency, respectively. Consequently, the nutrients concentration discharged in superficial water bodies was not compatible with the Brazilian standards of CONAMA 357/08 and 301/88 COPAM. However, the STP's performance was in accordance to the original designed configuration. The receiving water quality bodies were heavy polluted already at upstream sampling point and worsened at downstream because the effect of the final effluent discharge (increased water pollution degree). For few variables there was a decrease in the water body concentration due a dilution effect of final effluent discharge. The receiving water bodies presented a good potential for water reuse unrestricted, particularly for crop irrigation and can contribute for food production.